This invention relates to a novel method of manufacturing 1,1,1,3,3-pentafluoropropane, CF.sub.3 CH.sub.2 CF.sub.2 H, which is referred to in the art as HFC-245fa. Specifically, the invention relates to the fluorination with hydrogen fluoride of a compound of the formula: EQU CF.sub.y Cl.sub.3-y CH.sub.2 CHF.sub.w Cl.sub.2-w
wherein w=0, or 1, and y=0-3, in the presence of a fluorination catalyst to produce HFC-245fa.
HFC-245fa has physical properties, including a boiling point of about 14.degree. C., which make it particularly attractive as a blowing agent. (See Ger. Often, DE 3,903,336, 1990 (EP 381,986 A)). It also has the ability to function as an aerosol propellant (U.S. Pat. No. 2,942,036 to Smith and Woolf) in a manner similar to trichlorofluoromethane, which is referred to in the an as CFC-11, and as a heat transfer agent. (Jpn. Kokai Tokyo Koho JP 02,272,086 in 114 Chemical Abstracts 25031q (1991)).
Traditionally, chlorofluorocarbons (CFCs) like CFC-11 and dichlorodifluoromethane (CFC-12) have been used as refrigerants, blowing agents and propellants. These materials, however, are believed to contribute to stratospheric ozone depletion. The fluorocarbon industry therefore has focused its attention on developing stratospherically safer alternatives to these materials. HFC-245fa is a candidate replacement material since it functions in substantially the same way as the CFCs but is zero ozone depleting. Because the demand for these and other low or zero ozone depleting materials will increase dramatically in the future, commercially viable processes for their preparation are needed.
Only two methods for manufacturing HFC-245fa (which are not hydrofluorination reactions) are reported in the art. However, these methods are not without their shortcomings. Knunyants, et at., Catalytic Hydrogenation of Perfluoro Olefins, 55 Chemical Abstracts 349f (1961), discloses the reduction of 1,1,1,3,3-pentafluoropropene to HFC-245fa. Because this process includes multiple steps, it is inefficient and uneconomical. Burdon, et at., Partial Fluorination of Tetrahydrofuran with Cobalt Trifluoride, J. Chem. Soc. (C), 1739 (1969), discloses the elemental fluorination of tetrahydrofuran to produce HFC-245fa. This process suffers the disadvantage that it produces a host of other by-products, thus reducing the yield of the desired product.
As far as hydrofluorination reactions are concerned, there are no such methods for the production of HFC-245fa reported in the art, let alone fluorination reactions which use 1,1,1,3,3-pentachloropropane (CCl.sub.3 CH.sub.2 CHCl.sub.2) as the starting material to produce HFC-245fa. Although the conversion of --CCl.sub.3 groups to --CF.sub.3 groups is well-known in the art, attempts to fluorinate terminal --CHCl.sub.2 or --CHClF groups to--CHF.sub.2 groups in compounds having more than two carbons, (in particular compounds of the formula RCH.sub.2 CHCl.sub.2 and RCH.sub.2 CHFX wherein X is Cl or Br and R is an alkyl group having at least one carbon atom), have not been successful. See Henne, et al., Fluoroethanes and Fluoroethylenes, 58 J. Am. Chem. Soc. 889 (1936).
Tarrant, et al., Free Radical Additions Involving Fluorine Compounds. IV. The Addition of Dibromodifluoromethane to Some Fluoroolefins, 77 J. Am. Chem. Soc. 2783 (1955) report the fluorination of compounds of the type CF.sub.2 BrCH.sub.2 CHFBr with hydrogen fluoride (HF) in the presence of a Sb(V) salt catalyst, such as SbCl.sub.5 and TaF.sub.5. However, this method produced only a 14% yield of CF.sub.3 CH.sub.2 CHFBr at 125.degree. C., and only a modest improvement in yield at 170.degree. C. Even at elevated temperatures, no HFC-245fa was produced.